This paper checks whether a striking line of faint dwarf galaxies near the big galaxy NGC 1052 is a real three‑dimensional structure or just a chance overlap with a nearer group of galaxies. The line includes two unusual ultra‑diffuse galaxies, NGC 1052‑DF2 and DF4, that appear to lack dark matter (DM). One proposed origin is a high‑speed, head‑on collision between two gas‑rich dwarf galaxies, a “bullet‑dwarf” event, which would naturally produce a linear trail of objects. But the trail sits on top of a foreground group around NGC 1035 at about 13 megaparsecs (Mpc), so the authors test whether the trail might be only an accidental projection effect.

The team used Hubble Space Telescope (HST) images to measure distances to eight candidate trail dwarfs and to the giant galaxies NGC 1052 and NGC 1035. For these faint targets they applied the surface brightness fluctuation (SBF) method. SBF measures how much the brightness of image pixels varies because of unresolved stars; this variation gets smaller for more distant galaxies, so it can be turned into a distance estimate. The HST data came from the Advanced Camera for Surveys and used two filters commonly called F606W and F814W. The SBF signal was measured mainly in F814W because it is most sensitive to the bright red giant stars that dominate the fluctuations.

Their main distance result is that the measured dwarfs lie at about 20 Mpc, not at the nearer 13 Mpc of the NGC 1035 group. That result supports the idea that the trail is a real structure near NGC 1052 and not a foreground artifact. However, one important case stands out. For DF2 the HST SBF distance is 17.7 ± 1.4 Mpc, which disagrees with a previously published HST distance of 21.7 ± 1.2 Mpc that used the tip of the red giant branch (TRGB) method. The authors also used new James Webb Space Telescope (JWST) data to measure DF2 with the TRGB method and found 17.6 ± 0.6 Mpc, in good agreement with the SBF result.